Programmable reference circuits have been developed and used in a variety of electronic devices. Such circuits can provide relatively stable reference voltages over a wide range of operating conditions. Amplifier circuitry and other circuits have been developed to enhance the accuracy of such reference voltages.
The most popular method for the implementation of voltage and current references is developed around the silicon energy bandgap. In such circuits, a reference current or voltage is derived from two p-n junctions operated at different current densities, each having a different forward bias voltage drop. Conventional circuits typically utilize voltage-mode architectures that require significant voltage head-room for reliable operation.
However, recent technological advances on deep sub-micron CMOS circuit implementation require reduced levels of operating voltages. Thus, voltage head-room has become increasingly limited, making it difficult to use conventional bandgap reference circuits. As a result, new reference architectures have been developed based on the current-mode approach.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items.